1. Field of the Invention
This invention relates to a focusing screen used in the finder of a still camera or a movie camera.
2. Description of the Prior Art
Conventional focusing screens for cameras are of the mat surface type, the microprism type or the split image type. Of these, the split image type has involved the necessity of properly making adjustment of the visibility of the eyepiece to properly effect focusing because, in case of an aerial image, the eye adjusts the focus even if the focus point of the lens is not coincident with the focal plane. Also, sufficient range finding accuracy has not been obtained unless a target perpendicular to the optical wedge has lain at the location whereat the split exists. The mat surface type has involved the necessity of improving the diffusion property of the mat surface in order to obtain sufficient range finding accuracy on the mat surface, but if the diffusion property is improved, the particulate character of the mat surface becomes conspicuous and the finder view field becomes remarkably dark to make focusing difficult to effect. The microprism type, when disposed on the entire focusing screen, can be adjusted anywhere with sufficient range finding accuracy, but the image at a location whereat the focus point is not adjusted has been unsightly and difficult to see. That is, in the conventional microprism type focusing screen, the pitch of the microprism is great as compared with the resolution of the eye and therefore, defocused image can be handled in the fashion of vernier visual power to provide considerably good range finding accuracy, but defocused image (out-of focus image) has been unsightly. To make this defocused image easier to observe, the pitch of the microprism can be made small, but if it is made too small, the feature that the defocused image becomes rugged will be lost to reduce the range finding accuracy.